1. Technical Field of the Invention
The present invention relates to a method for isolation of barely volatile organic compounds and an apparatus for carrying out of the method. The present inventions are useful for preparation of samples for analysis containing the barely volatile organic compounds, for example, dioxins, in test samples such as ashes.
2. Description of Related Art
Recoveries of dioxins are required to be more than 60% using an official method for quantitative analysis according to law. However the official method is very troublesome and also requires highly practiced techniques and expensive devices. In comparison of steam distillation (referred to as Method I below), Soxhlet extraction (Method II) and ultrasonic extraction (Method III), F.I. Onuska et al. report that the steam distillation method (Method I) was found to be the most efficient for determination of dioxins and the order of efficiency is Method I greater than II greater than III (F.I. Onuska and K. A Terry (Anal. Chem. 1985, 57, 801-805). The official method is Method II. Ramos et al. studied and reported on 14 polychlorinated biphenyls, 10 polychlorinated dibenzo-furans and 7 polychlorinated dibenzo-dioxins recovered according to Method I (J. Chromatogr. A, 690, (1995) 243-249). The recoveries were more than 60% for some compounds, however, not for all compounds.
Polychlorinated biphenyls, polychlorinated dibenzo-furans and polychlorinated dibenzo-dioxins as typical environmental pollutants (these three kinds of compounds are all together referred to as xe2x80x9cdioxinsxe2x80x9d by Environment Agency of Japan) and polychlorinated hydrocarbons such as Aldrin, chlordane and Dildrin as endocrine-disrupting chemicals (so-called environmental hormones) have become objects of public concern. Dioxins are also listed as endocrine-disrupting chemicals. In addition, dozens of chemicals are listed as environmental pollutants. According to co-analysis by high resolution gas chromatography and mass spectrometry (HRGC-MS), the recoveries of those compounds are required by official specification to be more than 60% using the official method. However, quantitative recoveries (i.e. almost 100%) of objective compounds (except non-volatile organic compounds) are desired.
For example, as to dioxins, 2,3,7,8-tetrachlorobenzo-p-dioxin (TCDD), 1,2,3,4,6,7,8,9-octachlorobenzo-p-dioxin (OCDD), 1,2,3,4,6,7,8,9-octachloro-dibenzofuran (OCDF), 2,3,4,7,8-pentachloro-dibenzofuran (PCDF) are mentioned as typical dioxins. Unless these dioxins can be recovered almost 100%, a method for isolation of the dioxins is not sufficient.
Ramos et al reported that PCDF was xe2x80x9cnot detectedxe2x80x9d in three recovery tests according to Method I. The toxic equivalency factor of the most toxic TCDD is 1.0 and that of PCDF is 0.5, that is, it should be noted that PCDF displays very strong toxicity and yet PCDF was xe2x80x9cnot detectedxe2x80x9d.
Now it has been found, surprisingly, that in a steam distillation of a barely volatile organic compound in a test sample, where a volatile solvent and super-heated steam are simultaneously and continuously added to the organic compound in a distillation pot, whereby azeotropic distillation is constantly carried out by the ternary system of the barely volatile organic compound, the volatile solvent and super-heated steam, the boiling point of the barely volatile organic compound is decreased and the organic compound is recovered almost 100% from the test sample.
Conventional steam distillation is carried out using feeding of steam and is azeotropic distillation of a binary system of vapor of compound of interest and water vapor. F.I. Onuska et al, after all, employed azeotropic distillation of binary system (Onuska et al., ibid.) and, to stretch a point, batch-wise steam distillation. L. Ramos et al used a distiller with two distillation arms connected to two separate flasks containing an aqueous sample solution and an extraction solvent, respectively. That is, in fact, they carried out azeotropic distillation of binary system of vapor of the sample and water vapor from the aqueous sample solution, and the solvent vapor was mixed with the sample vapor on a cool condenser surface and subjected to extraction (Ramos et al., ibid.). In other words, Onuska et al and Ramos et al carry out azeotropic distillation of a binary system, not of a ternary system.
In the method of the present invention, super-heated steam simultaneously with a volatile and hardly water-soluble/water insoluble solvent is continuously injected into a distillation pot containing a barely volatile compound in order to decrease the boiling point of barely volatile compound azeotropically. The method is undoubtedly steam distillation and a volatile solvent is also injected continuously to decrease the boiling point of the barely volatile compound. The method is an azeotropic distillation relying on a ternary system. Such a method is not known in the art.
The present invention provides a method for isolation of a barely volatile organic compound from a sample suspected to contain the same, which comprises continuously adding super-heated steam and a volatile and hardly water-soluble/water-insoluble solvent to a liquid or solid sample suspected to contain said organic compound to be isolated, a solid sample being dissolved in said solvent which can dissolve said organic compound to be isolated, distilling off as an azeotropic mixture of said organic compound and said solvent by steam distillation, separating thus obtained distillate into a solvent phase of said solvent dissolving said organic compound and a water phase, and recovering quantitatively said organic compound from said solvent.
Also the invention provides an apparatus for carrying out a method for isolation of a barely volatile organic compound from a sample suspected to contain the same, which comprises continuously adding superheated steam and a volatile and hardly water-soluble/water-insoluble solvent to a liquid or solid sample suspected to contain said organic compound to be isolated, a solid sample being dissolved in said solvent which can dissolve said organic compound to be isolated, distilling off as an azeotropic mixture of said organic compound and said solvent by steam distillation, separating thus obtained distillate into a solvent phase of said solvent dissolving said organic compound and a water phase, and recovering quantitatively said organic compound from said solvent. The apparatus, for example, comprises a distillation pot, a distillation column, a steam generator, a cooling device (water-cooled or air-cooled), a separator, a thermometer, a steam control valve, and a container for a volatile and hardly water-soluble/water-insoluble solvent.
The method of the invention is useful for isolation of barely volatile organic compounds, for example, barely volatile and toxic endocrine-disrupting chemicals (so-called environmental hormones), dioxins, which are contained in ashes, industrial wastes, foods, resinoids, water of rivers, lakes or lagoons, drinking water and the like. The method according to azeotropic steam distillation of the ternary system may employed for preparation of samples for analysis by gas chromatography (electron-capture detector), high resolution gas chromatography-mass spectrometry (HRGC-MS) and the like.
According to the present invention, by carrying out of steam distillation together with continuously adding hardly water-soluble/water-insoluble solvent to a test sample containing a barely volatile organic compound, which can be easily distilled off azeotropically, the temperature in a distillation pot does not rise to the extent that the organic compound is converted to resin, and therefore, the test samples can be efficiently treated. No toxic barely volatile organic compound is detected in the distilled water accompanied by the solvent and therefore, the method of the invention is safe for environment.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.